Research in our laboratory has been directed toward examining the properties of tRNA methyltransferases purified from rat mammary tumors. Our project is designed to define the characteristics of the tumor methyltransferases and to explore the relationship between altered methylating activity and tRNA methylation in neoplastic tissues. We are: (1)\studying the factors leading to diminished tRNA methylation at selected sites in tumors; (2)\comparing the structural and functional characteristics of purified tRNA methyltransferases from tumors and their normal counterparts; (3)\examining the relationship between mammalian tRNA methyltransferases and those from lower eukaryotes; and (4)\developing systems for producing antibodies to purified eukaryotic tRNA methyltransferases. (H)